If you want the colored gridlines to be the default for *every new
workbook*:
Open a new workbook
Goto Tools>Options>View tab>Gridlines color
Select the desired color
OK out
Save this file as your default:
Goto File>Save As
File name: Book
Save as type: Template (*.xlt)
Save in: your XLStart directory
Where that is on your computer I don't know. On my machine its path is:
C:\Program Files\Microsoft Office\Office10\XLStart